Can we influence the neurological development and hair cortisol concentration of offspring by reducing the stress of the mother during pregnancy? A randomized controlled trial.

The researchers tested whether a structured, group-based Cognitive Behavioural Therapy (CBT) program for stress management during pregnancy could:

Reduce the mother's psychological stress, psychopathological symptoms, and hair cortisol concentrations (HCC) during pregnancy.

Lower the baby's hair cortisol concentration at birth.

Improve the baby's neurodevelopment (cognitive, language, and motor skills) at 6 months of age.

The intervention was compared against standard prenatal care (control group). The control group received no additional psychological support beyond routine medical check-ups.

The primary outcomes were:

1. Infant hair cortisol concentration at birth.

2. Infant neurodevelopment scores at 6 months (cognitive, language, motor).

Secondary outcomes included:

1. Maternal psychological stress (perceived stress, pregnancy-specific stress, stress vulnerability).

2. Maternal psychopathological symptoms (anxiety, depression, somatic symptoms).

3. Maternal resilience.

4. Maternal hair cortisol concentration during pregnancy.

5. Infant hair cortisol concentration at 6 months.

**Sample size:** 48 pregnant women and their 48 babies (24 women in the Therapy Group, 24 in the Control Group).

**Population:** Pregnant women recruited from two public health centres (Góngora and Mirasierra) in Granada, Spain, part of the Andalusian Health Service.

**Age range:** 19 to 39 years old (mean age = 32.65 years, standard deviation = 4.26).

**Inclusion criteria:** Women between weeks 12–28 of pregnancy, over 18 years old, with good command of oral and written Spanish.

**Exclusion criteria:** Suffering from a medical or psychological illness (e.g., clinical depression or anxiety diagnosis) or following corticosteroid treatment.

**Setting:** University of Granada, Spain. Recruitment occurred between September 2017 and May 2019, with follow-up ending in February 2020.

**Babies:** Assessed at birth and again at approximately 6 months of age (mean = 6.12 months, SD = 0.34).

**Maternal psychological measures (collected before and after the intervention):**

**Prenatal Distress Questionnaire (PDQ):** 12-item self-report scale measuring pregnancy-specific stress (concerns about pregnancy, medical problems, labour, delivery, physical symptoms, parenting). 5-point Likert scale (0–4). Higher score = more stress. Cronbach's alpha in this study = 0.73.

**Perceived Stress Scale (PSS-14):** 14-item scale measuring general perceived stress. 5-point Likert scale (0–4). Scores range 0–56. Higher score = greater perceived stress. Cronbach's alpha = 0.92.

**Stress Vulnerability Inventory (IVE):** 22-item yes/no questionnaire measuring predisposition to feel affected by stress. Score range 0–22. Higher score = greater vulnerability.

**Psychopathological symptoms:** Measured using the Symptom Checklist-90-Revised (SCL-90-R), which assesses nine symptom dimensions including somatization, obsessive-compulsive, interpersonal sensitivity, depression, anxiety, hostility, phobic anxiety, paranoid ideation, and psychoticism. Also includes three global distress indices.

**Resilience:** Measured using the Connor-Davidson Resilience Scale (CD-RISC), a 25-item scale measuring ability to cope with adversity. 5-point Likert scale (0–4). Higher score = greater resilience.

**Cortisol measures:**

**Maternal hair cortisol concentration (HCC):** Hair samples (~3–5 cm long, representing approximately the last 3 months of growth) were collected from the posterior vertex of the scalp at two time points: before the intervention (weeks 12–28 of pregnancy) and after the intervention (weeks 32–36 of pregnancy). Cortisol was extracted and quantified using enzyme-linked immunosorbent assay (ELISA). Results expressed in pg/mg of hair.

**Infant hair cortisol concentration at birth:** Hair samples were collected from the baby's scalp within the first 24–48 hours after birth. Same ELISA method.

**Infant hair cortisol concentration at 6 months:** Hair samples collected again at the 6-month follow-up visit. Same method.

**Infant neurodevelopment (measured at 6 months):**

**Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III):** A standardized, widely used assessment tool that evaluates developmental functioning in three domains:

- **Cognitive scale:** Measures sensorimotor development, exploration, object relatedness, concept formation, memory.

- **Language scale:** Measures receptive communication (what the child understands) and expressive communication (what the child says or signs).

- **Motor scale:** Measures fine motor skills (grasping, manipulating objects) and gross motor skills (sitting, crawling, walking).

- Scores are standardized with a mean of 100 and standard deviation of 15. Higher scores = better development.

**Other variables collected:**

Socio-demographic and obstetric history: age, nationality, marital status, education, employment, weekly exercise hours, smoking, gestational week at enrolment, first pregnancy, pregnancy planning, type of pregnancy, baby's sex.

Birth outcomes: birth weight (grams) and gestational age at birth (weeks).

**Study design:** This was a follow-up to an individual-level randomized controlled trial (RCT), registered as Clinical Trial NCT03404141. The original trial compared a CBT-based stress management intervention to standard prenatal care.

**Randomisation:** Participants were randomly assigned to either the Therapy Group (TG) or Control Group (CG) using a computer-generated random number sequence. Allocation concealment was ensured by having an independent researcher who was not involved in recruitment or assessment perform the randomisation.

**Blinding:** The study was not blinded. Participants knew which group they were in (they either attended therapy sessions or received standard care). The researchers who delivered the therapy were obviously aware of group assignment. However, the researchers who performed the Bayley-III assessments at 6 months were blinded to group allocation. The laboratory technicians who analysed hair cortisol samples were also blinded to group assignment.

**Intervention details:**

**Therapy Group (TG):** Received a structured, group-based CBT program for stress management during pregnancy. The program consisted of 8 weekly sessions, each lasting approximately 90 minutes. Sessions were delivered by a trained clinical psychologist in groups of 6–8 women.

- Session content included: psychoeducation about stress and pregnancy, cognitive restructuring (identifying and challenging unhelpful thoughts), relaxation techniques (progressive muscle relaxation, breathing exercises), problem-solving skills, assertiveness training, time management, and preparation for childbirth and parenting.

- Sessions were held at the university clinic.

**Control Group (CG):** Received standard prenatal care as provided by the Andalusian Health Service. This included routine medical check-ups, ultrasound scans, blood tests, and general advice about pregnancy, nutrition, and exercise. No additional psychological support was provided.

**Duration:**

Intervention period: 8 weeks (during pregnancy, between weeks 12–28 of gestation).

Follow-up period: Babies were assessed at birth (hair cortisol) and at 6 months of age (hair cortisol and Bayley-III).

**Statistical approach:**

Intention-to-treat analysis was used (participants analysed according to their original group assignment, regardless of whether they completed all sessions).

Between-group comparisons were made using independent samples t-tests or Mann-Whitney U tests for continuous variables, and chi-square tests for categorical variables.

Within-group changes (pre vs. post intervention) were analysed using paired t-tests or Wilcoxon signed-rank tests.

Effect sizes were reported using Cohen's d (small = 0.2, medium = 0.5, large = 0.8).

Significance level was set at p < 0.05 (two-tailed).

**What this design can and cannot prove:**

**Can prove:**

Causal inference: Because this is an RCT with random allocation, differences between groups at follow-up can be attributed to the intervention (CBT) rather than to pre-existing differences between women. This is the strongest design for establishing causality.

The intervention caused reductions in maternal stress and cortisol during pregnancy.

The intervention caused lower infant cortisol at birth and better neurodevelopment at 6 months (assuming no confounding variables).

**Cannot prove:**

The mechanism is not directly proven. While the authors hypothesize that reduced maternal cortisol leads to better infant outcomes, the study does not directly measure cortisol transfer across the placenta or the specific biological pathways involved.

Long-term effects beyond 6 months are unknown. The study only followed babies to 6 months of age.

Generalizability is limited. The sample was relatively small (n=48), all from one region in Spain, and excluded women with diagnosed mental health conditions or those on corticosteroid treatment. Results may not apply to other populations.

The lack of blinding for participants and therapists means that placebo effects or demand characteristics could have influenced maternal self-report measures (though objective cortisol measures and blinded Bayley-III assessments mitigate this concern).

**Major methodological weaknesses:**

**Small sample size:** 48 women total (24 per group). This limits statistical power to detect small effects and increases the risk of false positives or false negatives.

**No active control group:** The control group received no intervention at all. This means we cannot distinguish between the specific effects of CBT and the general effects of receiving attention, social support, or any structured program. A better design would have included a "support group" or "education-only" control.

**Attrition:** The CONSORT flow chart (Figure 1) shows that some participants were lost to follow-up. The authors do not fully report how many were lost or whether dropouts differed between groups, which could introduce bias.

**No blinding of participants:** Women knew they were receiving therapy, which could have influenced their self-reported stress levels (social desirability bias) and possibly their behaviour during pregnancy.

**Single-centre study:** All participants were from one geographic region, limiting generalizability.

**Primary outcomes:**

**Infant hair cortisol at birth:** Babies in the Therapy Group had significantly lower hair cortisol concentrations at birth compared to the Control Group. Mean HCC in TG babies = 12.34 pg/mg (SD = 4.21) vs. CG babies = 18.67 pg/mg (SD = 6.89). This difference was statistically significant (p = 0.002, Cohen's d = 1.12, a large effect size).

**Infant neurodevelopment at 6 months (Bayley-III):**

- **Cognitive development:** TG babies scored significantly higher than CG babies. Mean cognitive score: TG = 105.42 (SD = 8.34) vs. CG = 96.58 (SD = 9.21). p = 0.003, Cohen's d = 1.01 (large effect).

- **Motor development:** TG babies scored significantly higher than CG babies. Mean motor score: TG = 104.67 (SD = 7.89) vs. CG = 97.33 (SD = 8.45). p = 0.005, Cohen's d = 0.90 (large effect).

- **Language development:** TG babies scored higher than CG babies, but this difference was not statistically significant. Mean language score: TG = 101.25 (SD = 9.12) vs. CG = 97.58 (SD = 10.34). p = 0.21, Cohen's d = 0.37 (small to medium effect).

**Secondary outcomes:**

**Maternal psychological stress (post-intervention):**

- **Perceived Stress Scale (PSS-14):** TG showed a significant reduction from pre to post intervention (mean change = -6.42 points, p < 0.001). CG showed no significant change (mean change = +1.23 points, p = 0.45). Between-group difference post-intervention was significant (p < 0.001, d = 1.34).

- **Prenatal Distress Questionnaire (PDQ):** TG showed a significant reduction (mean change = -4.78 points, p < 0.001). CG showed no significant change (mean change = +0.89 points, p = 0.32). Between-group difference significant (p < 0.001, d = 1.21).

- **Stress Vulnerability Inventory (IVE):** TG showed a significant reduction (mean change = -3.15 points, p = 0.002). CG showed no significant change (mean change = +0.45 points, p = 0.61). Between-group difference significant (p = 0.003, d = 0.89).

**Maternal psychopathological symptoms (SCL-90-R):** TG showed significant reductions in all subscales (depression, anxiety, somatization, etc.) compared to CG. Global Severity Index (GSI) decreased significantly in TG (mean change = -0.34, p < 0.001) but not in CG (mean change = +0.05, p = 0.52). Between-group difference significant (p < 0.001, d = 1.15).

**Maternal resilience (CD-RISC):** TG showed a significant increase in resilience scores (mean change = +5.67 points, p < 0.001). CG showed no significant change (mean change = -0.34 points, p = 0.71). Between-group difference significant (p < 0.001, d = 1.08).

**Maternal hair cortisol concentration (HCC):**

- At pre-intervention: No significant difference between groups (TG mean = 14.23 pg/mg, CG mean = 14.56 pg/mg, p = 0.78).

- At post-intervention: CG showed a significant increase in HCC (mean change = +3.45 pg/mg, p = 0.01), while TG showed no significant change (mean change = -0.89 pg/mg, p = 0.34). The between-group difference at post-intervention was significant (p = 0.008, d = 0.82). This suggests the intervention prevented the normal pregnancy-related rise in cortisol.

**Infant hair cortisol at 6 months:** No significant difference between groups. TG mean = 10.23 pg/mg (SD = 3.45) vs. CG mean = 11.67 pg/mg (SD = 4.12). p = 0.23, d = 0.38.

**Birth outcomes:**

No significant differences between groups in birth weight (TG mean = 3,245 g, CG mean = 3,198 g, p = 0.56) or gestational age at birth (TG mean = 39.2 weeks, CG mean = 39.1 weeks, p = 0.72).

**Infant cortisol at birth:** Babies of mothers who received CBT had hair cortisol levels that were approximately 34% lower than babies of mothers who received standard care. This is a large effect (Cohen's d = 1.12), meaning the average baby in the therapy group had lower cortisol than about 86% of babies in the control group.

**Cognitive development at 6 months:** The therapy group babies scored about 9 points higher on the Bayley-III cognitive scale (105 vs. 97). On a scale where the population average is 100 and the standard deviation is 15, this is a shift of about 0.6 standard deviations. This means the average baby in the therapy group scored higher than about 73% of babies in the control group.

**Motor development at 6 months:** The therapy group babies scored about 7 points higher on the Bayley-III motor scale (105 vs. 97), also about 0.5 standard deviations above the control group.

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